In a telecommunications service network, traffic may be classified by traffic type. For example, in an asynchronous transfer mode (ATM), network there are different classes of traffic, such as constant bit rate (CBR) traffic, variable bit rate (VBR) traffic, available bit rate (ABR) traffic, and unspecified bit rate (UBR) traffic. Traffic may be characterized for purposes of admission control, traffic shaping and management, and/or packet scheduling. Different classes of traffic may have a particular set of quality of service (QoS) requirements and traffic characteristics.
QoS is the ability to provide different priority to different applications, users, or data flows, or to guarantee a certain level of performance to a data flow. Requirements included in QoS are requirements for all aspects of a connection, including service response time, loss, signal-to-noise ratio, cross-talk, echo, interrupts, frequency response, loudness, and other requirements. A certain level of performance may be guaranteed. These QoS guarantees may be important if the network capacity is insufficient. In packet switched networks, QoS is affected by human factors, such as stability of service, availability of service, delays and user information. Also, QoS is affected by technical factors such as reliability, scalability, effectiveness, maintainability, and grade of service.